1. Field of the Invention
The present invention relates to an encoding device, an encoding method, a recording medium, and an image processing apparatus, and is preferably applied to an image processing apparatus such as an encoder or the like which encodes image data in accordance with an encoding method, for example, such as MPEG (Moving Picture Experts Group) or the like.
2. Description of the Related Art
Heretofore, a technique has been widely used wherein image data is encoded by an encoder to be recorded or distributed, and is decoded by a decoder at the time of displaying an image thereof. In recent years, increased resolution and increased frame rates of image data has led to an increase in the information volume of this image data. Therefore, with image processing apparatuses, a great amount of image data has to be handled within a certain period of time despite restricted resources such as memory, computing power, and so forth, included in the image processing apparatuses.
In the case of subjecting image data to some sort of image processing, such as shown in FIG. 1, an image processing apparatus R1 temporarily stores image data BL supplied thereto in memory 4. Subsequently, an image processing unit 2 reads out desired image data BL from the memory 4 in sync with image processing timing, thereby subjecting this image data to image processing.
Note however, the image processing apparatus R1 stores the image data BL in the memory 4 in certain increments, e.g., for each picture, and accordingly, has to read out the whole picture from the memory 4 even in the case of using only part of data within a picture. In general, the data amount of image data is great, and accordingly, the image processing apparatus R1 has to have great storage capacity as the memory 4, and also has to secure a wide bus bandwidth. As a result thereof, with the image processing apparatus R1, the system increases in size, and reduction in costs is difficult.
Therefore, a method has been proposed wherein the image data BL of which the data amount is reduced by encoding processing is stored in the memory 4 (e.g., Japanese Patent No. 3918263).
With the image processing apparatus 1S described in Japanese Patent No. 3918263, such as shown in FIG. 2, the image data BL is temporarily encoded, and is stored in the memory 4 in a state wherein the data amount thereof is reduced. At this time, the image processing apparatus 1S encodes the image data by dividing into small block increments, and stores these in the memory 4.
Subsequently, such as shown in FIG. 3, the image processing apparatus 1S reads out the encoded image data BL from the memory 4 in increments of blocks, and also decodes the encoded image data BL, and subjects this to image processing by the image processing unit 2.
Specifically, such as shown in FIGS. 4A and 4B, the image processing apparatus 1S executes encoding by a DPCM (Differential Pulse Code Modulation) circuit 10. The DPCM circuit 10 quantizes, for example, a pixel value made up of 8 bits into 6 bits by obtaining the difference between adjacent pixels values. At this time, the first pixel still has 8 bits since no difference value occurs.
Accordingly, the image processing apparatus 1S can reduce data in increments of blocks of five pixels made up of 8 bits (i.e., 40 bits), to 32 bits in total, which is ⅘ the data amount, for example. That is to say, with the image processing apparatus 1S, the image data BL is encoded in increments of small blocks and is stored in the memory 4, whereby random access as to the memory 4 can be executed, and the bus band can be reduced. Also, with the image processing apparatus 1S, according to reduction in data amount by encoding, the memory capacity of the memory 4 can be reduced. Also, the DPCM processing is simple encoding processing, and accordingly, does not deteriorate memory access efficiency.